RURAL ENGINEERING. 287 



RURAL ENGINEERING. 



Reclamation of the southern Louisiana wet prairie lands, A. D. Morehouse 

 {U. 8. Dcpt. Agr., Office Expt. Stas. Rpt. 1909, pp. Jfl5-439, pis. 5, figs. 6').— 

 This article is based on reports of investigations made during 1909 and 1910 by 

 A. M. Shaw, W. B. Gregory, and C. W. Okey. 



The formation of the alhivial lands is first taken up, the natural levees along 

 the bayous and streams discussed, and profiles given illustrating some of the 

 typical forms. The purpose of the investigations was to determine the volume 

 of water, or percentage of the rainfall, which it is necessary to pump from the 

 fields in order to secure adequate drainage of these soils; the area of the field 

 surface occupied by ditches, and the depth, width, and arrangement of the 

 ditches and levees required in a drainage system ; the influence of bad physical 

 condition of ditches upon the efficiency of the system; the distance from the 

 ground surface at which the water table should be maintained ; the difference 

 in the level of the water in the ditches while the pumps were in operation ; and 

 the percentage of saturation or the quantity of water which the soil should 

 contain when in the best condition for growing crops. 



To carry out the investigations four reclaimed tracts of land were chosen, 

 three equipped with pumping plants of ample capacity antl the fourth having a 

 gravity outlet. Rain gages were established on all of these tracts and by rating 

 the pumping plants the amount of water removed during the course of a year 

 was estimated, except in one case where the water was measured by means of a 

 weir and automatic water register. 



The results of measurements of rainfall and run-off show that for the mouths 

 from June to December, 1909, inclusive, the average percentage of run-off to 

 rainfall for the four tracts was 35, ranging from 43.7 to 9.99 per cent, the latter 

 tract not including a 5-in. rainfall of the first part of June, and also not being 

 as thoroughly ditched or in cultivation. Comparing the daily rainfall and 

 run-off and also the daily pumping record for 1907 and 190S for one plantation, 

 it was found that during 1907 it took 1-1.8 hours' pumping for each inch of the 

 66.32 in. of rainfall, whereas in 1908 the pumps ran 12.9 hours per inch for the 

 51.06 in. of rainfall. This indicates that the uneven distribution of the rainfall 

 throughout a year, as well as the fact that one part of the plantation may re- 

 ceive a very heavy precipitation during certain storms while only a small 

 shower may affect the rest of the land, has but slight effect on the general 

 yearly average, and that year by year the ratio of the necessary pumping to 

 the rainfall will be fairly constant. 



Methods of reclamation are considered under the heads of early methods, 

 levees and seepage, canal systems, interior ditch systems, and pumping plants. 

 Where a tract does not adjoin a bayou or other good outlet, it is necessary to 

 construct outfall canals. The tract is next surrounded by a low levee to pre- 

 vent flooding and ordinarily a large reservoir canal is constructed along the 

 inside of the levee nearest the outlet, and at some convenient point on this 

 canal the pumping plant is established. Connected with the reservoirs are col- 

 lecting ditches of somewhat smaller size, and at right angles to these latter 

 are lateral ditches which are still smaller. Ordinarily the main reservoir 

 canals range in width from 30 to 60 ft. and in depth from 5 to 8 ft. The deeper 

 the canal the greater storage capacity it possesses and the better outlet it fur- 

 nishes for the collecting ditches or laterals. For the tracts under consideration 

 this reservoir capacity amounted to from 0.1 to 0.4 in. of rainfall over the entire 

 area. The proportion of land occupied by the interior ditch system varied 

 from 3 per cent to nearly 6 per cent of the land surface. The collecting ditches 

 range from 4 to 10 ft. in width and from 4 to 5 ft. in depth, while the lateral 



77543°— No. 3—11 7 



